/// 输出
fn main() {
    println!("Hello, world!");
    println!("测试1");
    let _var = "this is class1";
    println!("哈哈，{0}---{1}", _var,12);

    let  a = "123";
    println!("{}",a.len());
    let a = a.len();
    println!("{}",a);
}
